Yeah, the issue being that Electrum is trying to support Lightning... which is where I believe the "expiry" time has more relevance.
I don't think this two features are connected though. The payment requests and their expiration time existed long before Lightning Network or its addition to Electrum.
P.S. I think part of the confusion may be because of the name of the tab (ie. Receive). Maybe if it were renamed to something like "Invoices" it could reduce the confusion at least.